From c066f205180636aecbdbd04e680309b520fdeb66 Mon Sep 17 00:00:00 2001
From: Aikar <aikar@aikar.co>
Date: Fri, 27 May 2016 21:41:26 -0400
Subject: [PATCH] Ensure Chunks never ever load async

Safely pushes the operation to main thread, then back to the posting thread

diff --git a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
index 7b7a3d0..9aaca21 100644
--- a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
+++ b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOExecutor.java
@@ -4,6 +4,7 @@ import com.destroystokyo.paper.PaperConfig;
 import net.minecraft.server.Chunk;
 import net.minecraft.server.ChunkProviderServer;
 import net.minecraft.server.ChunkRegionLoader;
+import net.minecraft.server.MCUtil; // Paper
 import net.minecraft.server.World;
 import org.bukkit.craftbukkit.util.AsynchronousExecutor;
 
@@ -14,7 +15,7 @@ public class ChunkIOExecutor {
     private static final AsynchronousExecutor<QueuedChunk, Chunk, Runnable, RuntimeException> instance = new AsynchronousExecutor<QueuedChunk, Chunk, Runnable, RuntimeException>(new ChunkIOProvider(), BASE_THREADS);
 
     public static Chunk syncChunkLoad(World world, ChunkRegionLoader loader, ChunkProviderServer provider, int x, int z) {
-        return instance.getSkipQueue(new QueuedChunk(x, z, loader, world, provider));
+        return MCUtil.ensureMain("Async Chunk Load", () -> instance.getSkipQueue(new QueuedChunk(x, z, loader, world, provider))); // Paper
     }
 
     public static void queueChunkLoad(World world, ChunkRegionLoader loader, ChunkProviderServer provider, int x, int z, Runnable runnable) {
diff --git a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOProvider.java b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOProvider.java
index b5efb9c..ef9529a 100644
--- a/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOProvider.java
+++ b/src/main/java/org/bukkit/craftbukkit/chunkio/ChunkIOProvider.java
@@ -35,8 +35,8 @@ class ChunkIOProvider implements AsynchronousExecutor.CallBackProvider<QueuedChu
 
     // sync stuff
     public void callStage2(QueuedChunk queuedChunk, Chunk chunk) throws RuntimeException {
-        if (chunk == null) {
-            // If the chunk loading failed just do it synchronously (may generate)
+        if (chunk == null || queuedChunk.provider.chunks.containsKey(ChunkCoordIntPair.a(queuedChunk.x, queuedChunk.z))) { // Paper - also call original if it was already loaded
+            // If the chunk loading failed (or was already loaded for some reason) just do it synchronously (may generate)
             queuedChunk.provider.originalGetChunkAt(queuedChunk.x, queuedChunk.z);
             return;
         }
-- 
2.9.3